"The Life of Julius Caesar," Plutarch's Lives of the
Noble Grecians and Romanes; translated by Sir Thomas
North (1579) - "The Life of Marcus Brutus," "The Life of
Julius Cæsar," and "The Life of Marcus Tullius Cicero"

Possible sources:

The First Booke of the Annales of Cornelius
Tecitus; translated by R. Grenewey (1598)

The Civil Wars, Appian of Alexandria, translated
by W.B. (1578)

Cæsar's Revenge, Anon. (1607)

Il Cesare, Orlando Pescetti (1594)

Analogues:

Cæsar Interfectus, Richard Eedes

The Myrroure for Magistrates, - Caius Julius
Cæsar, J. Higgins (1587)

The Governour, Sir Thomas Elyot (1531)

The Histories of Sallust; translated by Thomas
Heywood (1608)

The Roman History of Velleius Paterculus;
translated by Sir R. LeGrys (1632)

The Chronicles of England, Scotland, and Ireland,
Raphael Holinshed (1587 edn.) - "The Chronicle of Scotland"
(Macbeth)", "The Description of Scotland (Ancient Scottish
customs)," "The Chronicles of England (Young Siward)", and
"The Chronicles of England (Edward the Confessor)"

Probable source:

Rerum Scoticarum Historia, George Buchanan

Possible sources:

De Origine, Moribus, et Rebus Gestis Scotorum,
John Leslie (1578)

Medea, Seneca; translated by John Studley (1566)

Agememnon, Seneca; translated by John Studley
(1566)

Analogues:

Vertumnus Sive Annus Recurrens, Matthew Gwinn
(1607)

A Continuance of Albions England, William Warner
(1606)

An Alphabet of Tales, Estienne de Besançon.

The Chronicle of Andrew Wyntoun

[The Show of Kings]
- A Defensative against the Poyson of Supposed
Prophecies, Henry Howard (1583)
- A Letter of Nicolas Pasquier

Footnotes

Titus Andronicus

The History of Titus Andronicus. Anon. n.d. - The
Tragical History of Titus Andronicus

Plutarch's Parallel Lives; translated by Sir
Thomas North (1579) - (The Life of Scipio Africanus)

Analogues:

A Lamentable Ballad, Anon.

The History of Titus Andronicus. Anon. n.d. - The
lamentable and Tragical History of T. Andronicus (ballad)

Romeo and Juliet

Source:

The Tragicall Historye of Romeus and Juliet,
Ar[thur] Br[ooke] (1562)

Julius Caesar

Sources:

"The Life of Julius Caesar," Plutarch's Lives of the
Noble Grecians and Romanes; translated by Sir Thomas
North (1579) - "The Life of Marcus Brutus," "The Life of
Julius Cæsar," and "The Life of Marcus Tullius Cicero"

Possible sources:

The First Booke of the Annales of Cornelius
Tecitus; translated by R. Grenewey (1598)

The Civil Wars, Appian of Alexandria, translated
by W.B. (1578)

Cæsar's Revenge, Anon. (1607)

Il Cesare, Orlando Pescetti (1594)

Analogues:

Cæsar Interfectus, Richard Eedes

The Myrroure for Magistrates, - Caius Julius
Cæsar, J. Higgins (1587)

The Governour, Sir Thomas Elyot (1531)

The Histories of Sallust; translated by Thomas
Heywood (1608)

The Roman History of Velleius Paterculus;
translated by Sir R. LeGrys (1632)

Macbeth

Source:

The Chronicles of England, Scotland, and Ireland,
Raphael Holinshed (1587 edn.) - "The Chronicle of Scotland"
(Macbeth)", "The Description of Scotland (Ancient Scottish
customs)," "The Chronicles of England (Young Siward)", and
"The Chronicles of England (Edward the Confessor)"

Probable source:

Rerum Scoticarum Historia, George Buchanan

Possible sources:

De Origine, Moribus, et Rebus Gestis Scotorum,
John Leslie (1578)

Medea, Seneca; translated by John Studley (1566)

Agememnon, Seneca; translated by John Studley
(1566)

Analogues:

Vertumnus Sive Annus Recurrens, Matthew Gwinn
(1607)

A Continuance of Albions England, William Warner
(1606)

An Alphabet of Tales, Estienne de Besançon.

The Chronicle of Andrew Wyntoun

[The Show of Kings]
- A Defensative against the Poyson of Supposed
Prophecies, Henry Howard (1583)
- A Letter of Nicolas Pasquier